Kenneth Branagh works the room like a true luvvie, greeting his Wallander co-stars and crew with kisses, waves and handshakes. He’s scrubbed up well in a charcoal suit and purple shirt, but that’s not the only reason he’s glowing. Rather, the preview screening of the new series of his detective show – which airs on BBC1 tomorrow and is based on the books by Swedish author Henning Mankell – comes just two days after the boy from Belfast was awarded a knighthood in the Queen’s birthday honours.

Branagh (we can call him that until he visits the palace) said on the day of the announcement that his heart was “fit to burst”, and he seems no less excited about it now. “I’ve had a weekend of loveliness,” he says in a voice which is much quieter than you’d expect from such a thespian.

“The response has been overwhelming from people I haven’t seen for a trillion years: old school friends, people from all over the world … I’ve been touched.”

Branagh, 51, turned down a CBE in 1994, but there was no such hesitation over the knighthood.

“You think of all the people in your 30-year career who you’ve worked with, and you know they would be so made up, as indeed they have been at the acknowledgment of that work, so it seemed the right thing to say, ‘I appreciate that’,” says the actor.

And what a 30 years it’s been. Branagh started winning plaudits for his theatre work in the early 1980s after training at Rada. His family had moved to England from Northern Ireland when he was at school.

His first film role was as an uncredited extra in 'Chariots of Fire' in 1981, before TV work and the part of James Moon in 1987’s 'A Month in the Country'. In 1989 he directed and starred in 'Henry V', which earned him Oscar nominations for best actor and best film.

His canon features directing other works by Shakespeare, while roles include Benedick in 'Much Ado About Nothing', alongside his then-wife Emma Thompson, and 'Hamlet', in which he starred with Kate Winslet, Derek Jacobi and Julie Christie.

He appears to have distanced himself from the Bard in recent years, appearing in projects as diverse as 'Harry Potter and the Chamber of Secrets', 'Valkyrie' and 'My Week with Marilyn'. The last of those garnered him a number of best supporting actor nominations, including another Oscar tip, for playing Lawrence Olivier, an actor with whom he is often compared.

Although much of his career has been played out on the stage and big screen, it’s his recent small-screen role which has earned him a surprising amount of praise, as well as bringing Branagh plenty of critical plaudits – including Bafta TV and Emmy awards, as well as being named best actor at the 35th Broadcasting Press Guild Television and Radio Awards for the role.

In contrast to his bombastic Henry V or his clownish Benedick, Branagh’s Wallander is alarmingly aloof. The troubled detective in the Sweden-set crime drama is a man of few words but many emotions and Branagh gives a wonderfully stripped-back performance.

“There’s nothing superficial about him,” says Branagh, who’s obviously given a lot of thought to Mankell’s elusive creation. “He doesn’t really do banter … there’s no small talk. Many might say it’s sheerly miserable but there’s a seriousness and preoccupation about him.”

The actor has described Wallander as “an existentialist who is questioning what life is about and why he does what he does every day, and for whom acts of violence never become normal”.

Branagh has had plenty of time to get under the skin of the detective: his involvement in the series goes back to the inception of the project, meeting with Mankell in 2007 to discuss playing the role.

Despite living and breathing the character on and off since 2008 – the first time that the novels had been adapted into an English-language production – Branagh admits that even he was taken aback by the new series, which opens with a 90-minute film in which Wallander investigates a crime very close to home.

“This particular one is a very raw 90 minutes. When I read it I thought it was the bleakest thing I had ever read. I remember standing on the side of the road during filming and my producer said, ‘Can we really put this out on Sunday night?’ And yet there’s something so compelling about it,” he says.

Wallander faces several personal challenges in this opening episode. Not only is one of the crimes a bit too close for comfort, but he finds the semblance of happiness he’s allowed himself (he’s moved to a country house with his new partner, her son and a dog) is threatened by his all-consuming approach to solving crime.

“What’s touching about this episode is he is embracing the chance for a relationship, but the old dog can’t be taught new tricks,” explains Branagh.

It’s a trait he shares with fellow Scandinavian detective Sarah Lund from 'The Killing', another character who fascinates Branagh, and another unexpected hit for the BBC, its first series scoring higher viewing figures than US drama 'Mad Men'.

“I loved the second series very much,” he nods. “Who knew Scandicrime would turn out to be a genre? People seem to like battered, thinking, feeling people coming up against crime and everything that it embodies.”

Branagh admits to getting caught up in a box set like the rest of us. “You suddenly watch three in a night, then four, then think, ‘Blimey, it’s midnight!’. But having seen 'The Killing' and done this, I’d be happy watching a box set of 'Carry On' films for a while.”

The actor is hoping to make three more Wallanders before they “put him to bed”, and will take on more directing, having got behind the camera for the Marvel-character film 'Thor', though he will not be returning for its sequel.

A project based on another Mankell book, starring Jack Nicholson and Dame Judi Dench, has been sidelined because of scheduling conflicts, as has a film adaptation of 'The Guernsey Literary and Potato Peel Pie Society' (“so hard to explain in America”) in which Winslet was due to star.

More promising, however, is an as-yet-unnamed adaptation of one of Tom Clancy’s Jack Ryan novels.

“Yes, I should be directing that,” says Branagh. “It’s a prequel to how you might have seen the character as played by Ben Affleck and Alec Baldwin. It takes him from Wall Street, where he is working covertly, into a global adventure that puts lots of scary things at stake.”

By that time he might have felt the weight of the Queen’s sword on his shoulder, and with it the addition of that three-letter word to his name. So will he be insisting on being called Sir Kenneth?

“No!” he exclaims, suddenly projecting his voice. “I want to be called Kenneth.”